Back in 2011, the company announced its plans to develop the rocket—which is essentially three ‘Falcon 9s’, SpaceX’s most used vehicle, strapped together. Musk had expected the spacecraft to be ready by 2013.

“We tried to cancel the ‘Falcon Heavy’ program three times at SpaceX, because it [was] way harder than we thought,” he described after the launch.

National Geographic was present to film Musk and his crew in the moments leading to the milestone.

“Holy flying f***! That thing took off,” he cried. The team rushed outdoors and looked upwards. “Look at that! It’s unreal!”

Later in a press briefing, Musk recalled his unease as he watched the ‘Falcon Heavy’ prepare for lift-off. “Crazy things can come true. When I see a rocket lift off, I see a thousand things that could not work, and it's amazing when they do.”